The invention relates to motor vehicles in general, and more particularly to improvements in power trains for use in motor vehicles. Still more particularly, the invention relates to improvements in power trains which employ hydrokinetic torque converters with so-called bypass or lockup clutches.
Published German patent application Serial No. 44 31 640 discloses a power train wherein the hydrokinetic torque converter is installed between the rotary output element of an internal combustion engine and the input element of a change-speed transmission. The torque converter is particularly effective while the motor vehicle is being set in motion because, when the lockup clutch is disengaged, the torque converter ensures the achievement of a pronounced torque conversion. If the torque converter is not equipped or combined with a lockup clutch, losses at a high RPM of the internal combustion engine are very high, and this entails an unacceptably high fuel consumption. The lockup clutch is utilized to achieve savings in fuel and to improve the quality of emitted combustion products; such clutch is put to use to operate with slip or to be fully engaged when the engine RPM is high and the motor vehicle is operated at a high speed. This, in turn, entails the development of readily audible changes of RPM and/or readily detectable changes of pull and/or a readily detectable shock or tug in the power train of the motor vehicle. Such phenomena are, or are likely to be, a cause of considerable discomfort to the occupant or occupants of the motor vehicle. Moreover, the occupant or occupants of the motor vehicle cannot anticipate and/or influence the timing and/or the extent of engagement or disengagement of the lockup clutch.
When a torque converter is used in the power train of a motor vehicle, its load factor or load value (LW) is a preselected parameter which is determined by the equation LW=M.sub.pumpe /n.sub.motor.sup.2 wherein M.sub.pumpe is the torque of pump or impeller (hereinafter called pump) of the torque converter and n is the RPM of the internal combustion engine. Thus, the load factor LW is a function of the design and of the dimensions of the torque converter. It has been found that the fixed or predetermined load factor is or can be detrimental or can exert an undesirable influence upon the operation of the motor vehicle under certain circumstances of use including the velocity of the motor vehicle and/or the RPM ratios.
Accordingly, there exists an urgent need for power trains with improved hydrokinetic torque converter--lockup clutch combinations.